The present invention relates to a metal body discriminating apparatus for discriminating the material, shape, size, and the like of a metal object such as metal product, metal part, coin, etc. by using a magnetic field.
Hitherto, metal body discriminating sensors have been used, for instance, to discriminate a coin in an electronic coin detecting apparatus. Such apparatuses have been disclosed in JP-A-59-178592, JP-A-57-98089, JP-B-1-25030, International Publication W086/00410, U.S. patent application Ser. Nos. 4462513, 4493411, 4845994, and 4601380, and the like.
One typical example of such conventional electronic coin detecting apparatuses will be described hereinbelow with reference to FIGS. 15 to 19D. In FIG. 15, a coin 1, which has been inserted into the apparatus from a coin input port, rolls and moves in the electronic coin detecting apparatus along a guide rail 2 which is inclined downward to a front side A of the apparatus. The guide rail 2 has a width based on a thickness of the coins to be detected, an inclination angle, a flat surface, and the like so that the coin can roll smoothly. Movement in the lateral direction by the coin 1 is restricted by a side wall 3 which is formed perpendicularly to the surface of the guide rail 2 and a side plate (shown by a broken line) 4 which faces the side wall 3, thereby preventing the coin 1 from dropping from the guide rail 2.
The side wall 3 is slightly inclined in such a manner that when the coin 1 rolls along the guide rail 2, the coin 1 always slides against the surface of the side wall 3 due to the dead weight of the coin.
Detecting coils 5 and 6 are embedded in the side wall 3. A detecting coil 7 is embedded in the side plate 4 at a position which faces the detecting coil 5. The detecting coils 5 and 7 are provided in a positional relation such that when the coin 1 passes therebetween, the coils face almost the central portion of the coin. The detecting coil 6 is provided in a positional relation so as to face the peripheral portion of the coin 1 when the coin rolls therepast.
The detecting coils 5 to 7 are conventional metal body discriminating sensors. Each of the detecting coils has a copper wire 10 wound around a projecting portion 9 provided inside a cap-shaped ferrite core (pot core) 8 as shown in FIG. 16. The detecting coils 5, 6 and 7 are oriented in the side wall 3 and the side plate 4 so that each projecting portion 9 is directed toward a side of the coin 1 rolling therepast.
Each of the detecting coils 5, 6, and 7 detects the coin 1 with a detecting circuit combined with a bridge circuit as shown in, for instance, FIG. 17. That is, resistors r.sub.1 and r.sub.2 having predetermined resistance values and an adjusting resistor R.sub.1 and an adjusting coil L.sub.1 whose values have been preset to appropriate values are connected to form an oscillating circuit 11 of a predetermined frequency. A detecting coil L.sub.0 (corresponding to the detecting coil 5, 6, or 7) constitutes one side of the bridge circuit, whereby the circuit generates a detection signal S at a predetermined output contact.
Thus, as shown in FIG. 18, the detecting coils 5, 6, and 7 driven by the oscillating circuit 11 generate magnetic lines of force (shown by broken lines in the diagram) having predetermined magnetic flux densities and which extend into the path of the coin 1. The bridge circuit is set into an equilibrium state by changes in inductances and impedances of the detecting coils 5, 6, and 7 which are caused due to influences by eddy currents generated in the coin 1 when the coin 1 traverses the magnetic lines of force. Thus, a detection signal S which is indicative of a feature of the coin 1 is generated. The detecting coils 5 and 7 face each other and form a magnetic circuit (corresponding to an inductance L.sub.0 in FIG. 17), thereby generating magnetic lines of force which perpendicularly traverse the path of the coin 1. The coin 1 is detected when it passes through the magnetic lines of force. On the other hand, as shown in FIG. 18, the detecting coil 6 generates magnetic lines of force on one side of the path of the coin 1, so that the coin I is influenced by the magnetic lines of force only at one side thereof.
The coin detecting operation of the apparatus will now be described with reference to FIGS. 19A to 19D. The above diagrams show that when the coin 1 rolls toward the front side A along the guide rail 2, the detection signal S which is generated from the detecting circuit changes in accordance with changes in relative positions between the coin 1 and the detecting sensors 5 and 7.
When the coin 1 is away from the above detecting sensors as shown at a certain time point t.sub.1, the bridge circuit in FIG. 17 is not in its equilibrium state, so that a detection signal S (refer to FIG. 19B) having the same frequency f and amplitude H as those of the output signal of the oscillator 11 is generated.
As shown at a time point t.sub.2, when the front portion of the coin 1 moves inbetween the detecting coils 5 and 7, an eddy current is generated in that portion of the coin due to the magnetic lines of force, so that the inductance L.sub.0 of the bridge circuit changes and the amplitude of the detection signal S changes (refer to FIG. 19c). When the coin 1 further progresses between the detecting coils 5 and 7, the level of the eddy current which is generated also gradually increases and the amplitude of the detection signal S also changes in accordance with the change in eddy current.
As shown at a time point t.sub.3, when the central portion of the coin 1 coincides with the central portions of the detecting coins 5 and 7, the eddy current which is generated in the coin 1 becomes maximum and the amplitude of the detection signal S becomes minimum in accordance with the adjusting resistor R.sub.1 and the coil L.sub.1 (refer to FIG. 19D).
On the contrary, when the coin 1 moves away from the detecting coils 5 and 7, in a manner similar to the case shown in FIG. 19C, the amplitude of the detection signal S increases. After a time point t.sub.4 when the coin 1 is completely away from the detecting coils 5 and 7, the magnetic lines of force generated by the detecting coils 5 and 7 are not influenced by the coin 1. The amplitude of the detection signal S finally approaches the amplitude of the output signal of the oscillating circuit 11 in a manner similar to the case shown in FIG. 19B.
On the other hand, the detecting circuit associated with the detecting coil 6 also generates a detection signal S which changes in accordance with the portion of the coin 1 confronting the detecting coil 6 in a manner similar to the above case.
The detection signals S and s are analyzed and the diameter, thickness, material, deformation, and the like of the coin are judged from changes in the patterns and minimum amplitude values of the detection signals S and s, thereby discriminating a denomination, a fake coin, and the like.
The detection signal S which is generated by the detecting circuit using the detecting coils 5 and 7 is a signal which is indicative of the size, material, and thickness of the coin. The detection signal s which is generated by the detecting circuit using the detecting coil 6 is indicative of the thickness and diameter of the coin.
However, the metal body discriminating sensors comprising the detecting coils, and the metal body discriminating apparatus such as a coin detecting apparatus or the like using such sensors, have the following problems.
A coin or the like moves past the front surfaces of the detecting coils while rolling along the guide rail. If dust or dirt has been deposited on the guide rail due to environmental conditions surrounding the apparatus at the time of manufacture or with the lapse of time, the coin (metal body) won't roll smoothly on the guide rail but will jump thereon. In such a case, the positional relation between the metal body and the detecting coils is deviated from the normal state and the detection signals are distorted and an error occurs in the discrimination. That is, the guide rail functions as a reference surface to position the metal body such as a coin or the like and there is a drawback in that when the position of the metal body deviates from the position to be provided by the reference surface, the measurement cannot be performed with a high degree of accuracy.
Consequently, for instance, the maintenance of periodically cleaning the inside of the apparatus or the like is difficult and a cleaning apparatus or the like needs to be provided.
Further, the coin or the like must slide along the side wall 3 in order to move smoothly along the guide rail and to establish a set distance between the coin or the like and the detecting coil, i.e. to maintain a constant line when the coin or the like passes by the detecting coils. For this purpose, it is necessary to provide the inclination angle of the guide rail 2 and the inclination angle of the side wall 3 with a high degree of accuracy. Since the moving characteristics of the coin or the like also are affected by the material of the guide rail 2 and the material of the side wall 3, those materials also must be appropriately selected.
The intensities of the magnetic lines of force which are generated from the detecting coils 5 and 7 which face each other as shown in FIG. 18 are affected by the distance between the detecting coils 5 and 7. Therefore, the side wall 3 and the side plate 4 need to be held assembled accurately with a constant distance provided therebetween. In addition the detecting coils 5 and 7 must be embedded in the side wall 3 and the side plate 4 under a high degree of mechanical accuracy (i.e., small tolerance). It is, however, difficult to provide such accuracy and it is necessary to frequently execute adjustments. For instance, if a deformed coin or the like has become stuck on the guide rail, it is necessary to detach the side plate 4 and extricate the coin or the like. Therefore, the side wall 3 and the side plate 4 must often be reassembled, whereby their positional accuracy gradually deteriorates. Since such a deterioration influences the characteristics of the detection signals, the absolute measuring accuracy may become low. For instance, a coin detecting apparatus for discriminating Japanese coins is generally set to up to discriminate four kinds of coins. An adjusting device, a differential amplifier, and a comparator are thus needed for every denomination as will be obviously understood from FIG. 8 in JP-A-61-262990.
As mentioned above, in the metal body discriminating apparatus such as a coin detecting apparatus using conventional metal body discriminating sensors, to improve the detecting accuracy it is extremely important to improve the accuracy in the mechanical aspects, e.g. positional relationships of the elements, of the apparatus. There are so many problems to be solved that each apparatus must be individually adjusted, and the maintenance thereof is complicated, and like.